How to set Frame Range automatically to video length
Your problem - from a VSE point of view:

You want your End Frame Range to be set to your newly imported Footages length.
The solution:

While still hovering over the VSE view press PageUp.

Hover your mouse over your timeline and press E to match your End Frame with your Current frame. (Blenders Hotkeys are context sensitive)

Note:
Make sure, the function Use Preview Range is unchecked if you want your Scene Frame Range to be set accordingly for your final Render. 

Further explanation regarding your situation:
You want to achieve this in the MCE directly. Which is possible via some Python code. But for a quick manual workaround just import your MCE Clip into a VSE via Add (Shift+A) - Clip - &lt;Movie Clip Name&gt; as it will produce the result you want in the MCE as well. The Frame Range used is the current Scene ones which is applied to both the VSE and the MCE. You could delete your VSE Strip of the MCE clip afterwards if you don't want it to be rendered out.